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DB says: "The inverter the other person said he used in his system has a specified nominal efficiency of better than 90%."

This is not a true sine wave inverter. True sine wave inverters (often called synchronous inverters) are required for a utility grid tie in and run at far less efficiency than the unit you cite. Inverters running at the level of efficiency you referenced, are designed with switching power supplies that include heavy amounts of low pass filtering in order to simulate (but never actually achieve) a sine wave output. They are not capable of being tied to the utility grid, and either run as "stand alones" or tied only to a local power grid.

--Boot Hill

They are not capable of being tied to the utility grid, and either run as "stand alones" or tied only to a local power grid.

Like in DG applications, which is what solar is best at.

This is not a true sine wave inverter. True sine wave inverters (often called synchronous inverters) are required for a utility grid tie in and run at far less efficiency than the unit you cite. Inverters running at the level of efficiency you referenced, are designed with switching power supplies that include heavy amounts of low pass filtering in order to simulate (but never actually achieve) a sine wave output. They are not capable of being tied to the utility grid, and either run as "stand alones" or tied only to a local power grid.

OH MY GOD!!! Some call PG&E and let them know!!! I've been tied to their grid for about 3 years!!!

"This is not a true sine wave inverter. True sine wave inverters (often called synchronous inverters) are required for a utility grid tie in and run at far less efficiency than the unit you cite. Inverters running at the level of efficiency you referenced, are designed with switching power supplies that include heavy amounts of low pass filtering in order to simulate (but never actually achieve) a sine wave output. They are not capable of being tied to the utility grid, and either run as "stand alones" or tied only to a local power grid."

Not true. Here's one example that is designed for utility tie in that is 90% efficient and uses a switching design:

http://www.xantrex.com/support/docserve.asp?id=220

I do not understand what you mean by "Inverters running at the level of efficiency you referenced, are designed with switching power supplies that include heavy amounts of low pass filtering in order to simulate (but never actually achieve) a sine wave output." What does “but never actually achieve” mean??? One percent distortion, 0.001% distortion??? It is all a matter of degree. There are no limitations on how "pure" a sine wave a switching supply can produce. Now you're in an area of electronic engineering I know something about. PWM can achieve very low distortion sine waves at high power levels at high efficiencies. The amount of "low pass" filtering required is primarily defined by the ratio of the AC output frequency to the switching frequency and the desired amount of attenuation to that switching frequency and its related sampling artifacts.

Did you even bother to read the first link I provided?

Here's the manual for the GC 1000:

http://www.advancedenergy.com/Doc/gc1000installationmanualv2.31.pdf

It is in fact a grid tie inverter qualified for use in California. It does connect and back-feed into the public utility grid just as the original poster claimed. If your solar or wind array generates more power than your home needs it feeds the excess power back to the public grid just as he claimed. Using a switching supply and all… And over 90% efficient in the process… And that “super” pure sine wave required looks to be around 5% total harmonic distortion (total harmonic content of less than -26 dBc). Not all that pure in electronic land.